1. Field of the Invention
The present invention relates to fluid pressure regulators, and more particularly to a pressure regulator for regulating the fluid pressure in the transmission of an automotive vehicle.
2. Description of Related Art
Pressure control devices for use in a control system of an automatic transmission of a motor vehicle have been proposed in the past. For example, a typical pressure control device may include a housing encasing a magnetic coil and an armature control slide movable within a valve through which a pressure medium to be controlled passes.
A problem with some of these pressure control devices is that they are not resistant to contamination, which compromises their reliability. Another problem is that such devices are single-stage devices wherein a spool valve is in direct contact with (and moved by) the armature, which requires that the position of the spool must be indexed to that of the armature, which complicates the device. Also, the travel of the spool is limited by what the armature can accommodate. Still further, only magnetic forces are available to move the spool.
A main object of the invention is to provide a pressure control device that overcomes problems, such as those referred to above, exhibited by prior art devices.
Accordingly, in a pressure regulator contemplated by the invention, the spool valve is not connected to the armature. Instead, the armature operates a first stage poppet servo valve.
Further, servo pressure is determined by the force balance on the armature, and the resulting servo pressure force has to equal the sum of the magnetic force and a mechanical spring force.
Additionally, there is also a force balance on the spool valve, and the spool will move, changing control pressure until the control pressure plus spool spring force equals the servo pressure force.
Some of the advantages of a pressure regulator embodying the invention are as follows:
1. Large hydraulic forces are available to move the spool valve instead of low magnetic forces, which substantially improves response time and overcomes potential fouling. PA1 2. Since the position of the spool valve is independent of the position of the solenoid armature, large flows can be accommodated without pressure variation due to changes in armature position. PA1 3. Manufacturability is improved because there is no need to maintain a precise position between the armature and the spool valve and its ports. PA1 4. Hydraulic flow forces do not enter into the armature force balance and therefore do not have a large effect on the regulation of the device.
These and other objects and advantages of the invention will become more apparent by reference to the following specification and the attached drawings.